With highly-touted prescription diet drug Acomplia (Rimonabant) now on the market in Britain for about $3.50 per day, how much room does that leave for non-prescription Alli, a half-strength version of Xenical (orlistat), if it is approved as expected for over-the-counter sale later this summer?

That is the question a number of analysts are asking after Sanofi announced a lower-than-expected launch price in England for the first of the two diet drugs to make it to market this year.

With prescription Xenical, which is normally taken three times a day after meals, selling at the largest U.S. drugstore chain, Walgreen's, for $2.25 a pill (or $6.75 per day), analysts now project a considerably lower price for Alli (pronounced Al-EYE) of around 60 cents a pill (or $1.80 a day).

But considering that full-strength Xenical has been a major disappointment to dieters, how many people are going to turn to Alli, a pill that may help them lose a few pounds, instead of the not-that-much-more expensive Acomplia, which has helped articipants in trials lose 10 percent of their body weight.

The company that will market Alli, GlaxoSmithKline, is clearly hoping that the pill will benefit from the fact that following its expected U.S. Food and Drug Administration approval, Alli would be the only FDA-okayed non-prescription diet preparation on pharmacy and health-store shelves.

Glaxo's bet is that Alli will be purchased by overweight people who are unwilling to go to their doctor and risk a lecture about the need for a better diet and more exercise.

But the unexpectedly low launch-price of Acomplia in Britain -- coupled with stories hailing Acomplia as a "wonder drug" coupled with continuing tales of the side-effects of Xenical (flatulence and diarrhea) -- may leave the future of Alli very much in the air.